The present invention relates to a CPU cooling fan mounting structure which ensures stable operation of the CPU cooling fan.
In order to improve the heat dissipating efficiency of a CPU heat sink, a cooling fan is commonly used and installed in the CPU heat sink. As illustrated in FIG. 1, the heat sink 101 has a flat base 1011, an axle hole 1013 at the center of the flat base 1011, and a plurality of upright radiating fins 1012 raised around the four sides of the flat base 1011; the cooling fan 102 is mounted on the flat base 1011 of the heat sink 101. The fan motor 103 of the cooling fan 102 has a shaft 1032 extended out of the PC board 1031 and fitted into the axle hole 1013 on the flat base 1011 of the heat sink 101. When operated, the cooling fan draw cooling air from the top side into the heat sink and then driven it out of the heat sink 101 radially to carry heat away. As the heat sink 101 is made from aluminum alloy and the shaft 1032 of the fan motor 103 is made from steel, they have different coefficients of expansion. Therefore, the diameter of the axle hole 1013 will become slightly bigger when hot, causing the shaft 1032 of the fan motor 103 to oscillate in the axle hole 1013. When the shaft 1032 of the fan motor 103 oscillates in the axle hole 1013 during the operation of the cooling fan 102, noises will be produced. Frequently vibrating the shaft 1032 of the fan motor 103 will damage the periphery of the axle hole 1013, causing the diameter of the axle hole 1013 enlarged. When the diameter of the axle hole 1013 is enlarged permanently, the fan motor 103 of the cooling fan 102 may disconnect from the heat sink 101 easily.